Circuit device, light source device, and electronic apparatus

ABSTRACT

A circuit device includes an N-type well on a P-type substrate, a P-type well provided in the N-type well, a circuit element provided in the P-type well, a P-type well provided in an N-type well, and a circuit element provided in the P-type well. A ground power supply voltage is supplied to a P-type well. A power supply voltage different from the ground power supply voltage is supplied to a P-type well. The ground power supply voltage or a first potential that is greater than or equal to the potential of the ground power supply voltage and less than the potential of a high potential-side power supply voltage is supplied to an N-type well.

The present application is based on, and claims priority from JPApplication Serial Number 2019-140789, filed Jul. 31, 2019, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a circuit device, a light sourcedevice, an electronic apparatus, and the like.

2. Related Art

In an integrated circuit device, a triple well structure is known inwhich an N-type well is provided in a P-type substrate, and a P-typewell is provided in the N-type well. In JP-A-2014-027111, a knowntechnique of the triple well structure is disclosed. InJP-A-2014-027111, the impurity concentrations of an N-type well contactthat is in contact with an N-type well and a P-type well contact that isin contact with a P-type substrate are increased. With this, theresistance values of the N-type well and the P-type substrate arereduced, and as a result, occurrence of latch-up can be suppressed. InJP-A-2014-027111, the potential of the N-type well is set to a powersupply voltage by setting the potential of the N-type well contact tothe power supply voltage.

When a plurality of P-type wells whose potentials are different to eachother are desired to be used, a method is conceivable in which eachP-type well is isolated from a P-type substrate by an N-type well. Here,there is a problem that, unless the potentials of the N-type wells areappropriately set, element breakdown or an unexpected leak current mayoccur.

SUMMARY

One aspect of the present disclosure relates to a circuit devicecomprising: a first N-type well on a P-type substrate; a first P-typewell that is provided in the first N-type well and to which a firstground power supply voltage is supplied; a first circuit elementprovided in the first P-type well; a second N-type well on the P-typesubstrate; a second P-type well that is provided in the second N-typewell and to which a power supply voltage different from the first groundpower supply voltage is supplied; and a second circuit element providedin the second P-type well, wherein the first ground power supply voltageor a first potential that is greater than or equal to the potential ofthe first ground power supply voltage and less than the potential of ahigh potential-side power supply voltage is supplied to the first N-typewell.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 shows an exemplary configuration of a circuit device of a presentembodiment.

FIG. 2 is a first cross-sectional view of a semiconductor substrate ofthe circuit device when a high potential-side power supply voltage issupplied to an N-type well.

FIG. 3 is a second cross-sectional view of the semiconductor substrateof the circuit device when the high potential-side power supply voltageis supplied to the N-type well.

FIG. 4 is the second cross-sectional view of the semiconductor substrateof the circuit device when the high potential-side power supply voltageis supplied to the N-type well.

FIG. 5 is a first cross-sectional view of the semiconductor substrate ofthe circuit device of the present embodiment.

FIG. 6 is a second cross-sectional view of the semiconductor substrateof the circuit device of the present embodiment.

FIG. 7 is a cross-sectional view of an exemplary configuration ofmodification of a first circuit element.

FIG. 8 is a detailed cross-sectional view of the semiconductor substrateof the present embodiment.

FIG. 9 shows a first exemplary configuration of a light source device.

FIG. 10 is a waveform diagram in a PWM light modulation mode.

FIG. 11 shows a second exemplary configuration of the light sourcedevice.

FIG. 12 shows an exemplary configuration of an electronic apparatus.

FIG. 13 shows an exemplary configuration of a light source circuit.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a preferable embodiment of the disclosure will be describedin detail. Note that the embodiment given below is not intended tounduly limit the scope of the disclosure recited in the appended claims,and not all of the constituent elements described in the embodiment areessential to the disclosure.

1. Exemplary Circuit Configuration

FIG. 1 shows an exemplary configuration of a circuit device 100 of thepresent embodiment. Note that FIG. 1 shows an example of the circuitconfiguration of the circuit device 100, and the circuit configurationof the circuit device 100 is not limited to that shown in FIG. 1 . Thatis, the circuit device 100 need only include a first N-type well, afirst P-type well, a first circuit element, a second N-type well, asecond P-type well, and a second circuit element, which will bedescribed later with reference to FIG. 5 and the like.

The circuit device 100 shown in FIG. 1 includes a drive circuit 50, aninput/output cell 20, a regulator 30, a bidirectional diode 40,terminals TVIN, TVREF, TAGND, TVDR, and TPGND, and an output terminalTGATE. The circuit device 100 is an integrated circuit device called anIC (Integrated Circuit). The circuit device 100 is an IC manufactured bya semiconductor process, and is a semiconductor chip in which circuitelements are formed on a semiconductor substrate. The terminals of thecircuit device 100 are terminals for electrically connecting the circuitdevice 100 and devices outside the circuit device 100, and are pads of asemiconductor chip, for example.

A ground power supply voltage PGND is supplied to the terminal TPGNDfrom the outside of the circuit device 100, and a ground power supplyvoltage AGND is supplied to the terminal TAGND from the outside of thecircuit device 100. The ground power supply voltage AGND is a groundpower supply voltage that is different from the ground power supplyvoltage PGND. Specifically, a first ground power supply line connectedto the terminal TAGND and a second ground power supply line connected tothe terminal TPGND is not directly connected, being directly connectedmeaning being connected with no circuit element interposed therebetween,inside the circuit device 100, and are isolated to each other inside thecircuit device 100. That is, the first ground power supply line and thesecond ground power supply line are not connected inside the circuitdevice 100, or are electrically connected via a coupling circuit. InFIG. 1 , a ground node NAGND corresponds to the first ground powersupply line, and a ground node NPGND corresponds to the second groundpower supply line. FIG. 1 illustrates an example in which the firstground power supply line and the second ground power supply line areelectrically connected through a bidirectional diode 40, which is acoupling circuit.

A power supply voltage VDR is supplied to the drive circuit 50 as a highpotential-side power supply voltage, and the ground power supply voltagePGND is supplied thereto as a low potential-side power supply voltage.The drive circuit 50 drives a circuit element outside the circuit device100 by outputting an output signal GATE to the circuit element from theoutput terminal TGATE. The drive circuit 50 includes a P-type transistor51, an N-type transistor 52, and a predriver 55.

A source of the P-type transistor 51 is connected to a power supply nodeNVDR to which the power supply voltage VDR is supplied, and a drainthereof is connected to an output node NDQ of the drive circuit 50. Asource of the N-type transistor 52 is connected to the ground nodeNPGND, and a drain thereof is connected to the output node NDQ. Theground node NPGND is connected to the terminal TPGND. As a result of thepredriver 55 driving a gate of the P-type transistor 51 and a gate ofthe N-type transistor 52, the P-type transistor 51 and the N-typetransistor 52 outputs the output signal GATE.

The input/output cell 20 is an electrostatic protection circuit forprotecting circuits in the circuit device 100 from ESD (Electro StaticDischarge). The input/output cell 20 includes protection diodes 21 and22 and a resistor 25.

One end of the resistor 25 is connected to the output node NDQ of thedrive circuit 50, and the other end is connected to the output terminalTGATE. An anode of the protection diode 21 is connected to the groundnode NPGND, a cathode of the protection diode 21 and an anode of theprotection diode 22 are connected to the output terminal TGATE, and acathode of the protection diode 22 is connected to the power supply nodeNVDR.

The bidirectional diode 40 is provided between the ground node NAGND andthe ground node NPGND in order to keep the potential difference betweenthe ground power supply voltages AGND and PGND at a predetermined valueor less. The ground node NAGND is connected to the terminal TAGND. Thebidirectional diode 40 includes diodes 41 and 42.

An anode of the diode 41 and a cathode of the diode 42 are connected tothe ground node NAGND, and a cathode of the diode 41 and an anode of thediode 42 are connected to the ground node NPGND.

The regulator 30 generates the power supply voltage VDR from an inputpower supply voltage VIN with the potential of the ground power supplyvoltage AGND being the reference. The input power supply voltage VIN isinput to the terminal TVIN from the outside of the circuit device 100,and the potential thereof is higher than the potential of the powersupply voltage VDR. Specifically, the regulator 30 includes a P-typetransistor 31, resistors 32 and 33, and an operational amplifier 35.

The input power supply voltage VIN is supplied to the operationalamplifier 35 as a high potential-side power supply voltage, and theground power supply voltage AGND is supplied thereto as a lowpotential-side power supply voltage. A reference voltage VREF is inputto an inverting input node of the operational amplifier 35. Thereference voltage VREF is input to the terminal TVREF from the outsideof the circuit device 100. Alternatively, the reference voltage VREF maybe generated in the circuit device 100. A source of the P-typetransistor 31 is connected to a power supply node NVIN to which theinput power supply voltage VIN is supplied, and a drain thereof isconnected to the power supply node NVDR. One end of the resistor 32 isconnected to the power supply node NVDR, and the other end is connectedto one end of the resistor 33 and a non-inverting input node of theoperational amplifier 35. The other end of the resistor 33 is connectedto the ground node NAGND.

2. Case where Potential of N-Type Well is Set to Potential of HighPotential-Side Power Supply Voltage

Hereinafter, problems relating to the potential setting of the N-typewell will be described. A first cross-sectional view of a semiconductorsubstrate of a circuit device 101 when a high potential-side powersupply voltage is supplied to the N-type well is shown in FIG. 2 . Thecircuit device 101 is configured similarly to the circuit device 100shown in FIG. 1 , and some of the constituent elements of the circuitdevice 101 are shown in FIG. 2 . Note that a “p⁺ impurity region” and an“n⁺ impurity region” are also referred to as a P-type impurity regionand an N-type impurity region.

The circuit device 101 includes a P-type substrate 90, N-type wells 61and 62 in the P-type substrate 90, a P-type well 71 provided in theN-type well 61, a P-type well 72 provided in the N-type well 62, anN-type transistor 81 provided in the P-type well 71, and an N-typetransistor 82 provided in the P-type well 72.

A well is a region where impurities are injected into the P-typesubstrate 90, and that is provided under circuit elements or anotherwell. For example, a well is an impurity region that is provided so asto cover circuit elements or another well. The well is not limited to awell constituted by one impurity region, and may be a well in which aplurality of impurity regions are combined. For example, the well may beconstituted by a buried layer and an impurity region that extends from asubstrate surface to the buried layer.

The potential of the P-type substrate 90 is set to the potential of theground power supply voltage AGND through a p⁺ impurity region 95. Thepotential of the N-type well 61 is set to the potential of the powersupply voltage VDR through an n⁺ impurity region 65. The potential ofthe N-type well 62 is set to the potential of the input power supplyvoltage VIN through an n⁺ impurity region 66. That is, the N-typetransistor 81 is an N-type transistor included in a circuit thatoperates with the power supply voltage VDR, and the N-type transistor 82is an N-type transistor included in a circuit that operates with theinput power supply voltage VIN. Specifically, the N-type transistorincluded in the drive circuit 50 shown in FIG. 1 is envisioned as theN-type transistor 81. An N-type transistor included in the operationalamplifier 35 shown in FIG. 1 is envisioned as the N-type transistor 82.Note that the circuit elements on the P-type wells 71 and 72 are notlimited to N-type transistors, and may include a diode, resistor, and acapacitor, for example. In the following, a case where the circuitelements on the P-type wells 71 and 72 are N-type transistors will bedescribed as an example.

The potentials of the P-type well 71 and a source of the N-typetransistor 81 are set to the potential of the ground power supplyvoltage PGND. The potential of the P-type well 71 is set to thepotential of the ground power supply voltage PGND through a p⁺ impurityregion 75. The potentials of the P-type well 72 and a source of theN-type transistor 82 are set to a potential VX of a power supply voltagethat is different from the ground power supply voltage PGND. Thepotential of the P-type well 72 is set to the potential VX through a p⁺impurity region 76. The potential VX is the potential of the groundpower supply voltage AGND, for example. Alternatively, the potential VXmay also be a potential between the ground power supply voltage AGND andthe input power supply voltage VIN.

As described above, as a result of the P-type wells 71 and 72 areisolated from the P-type substrate 90 by the N-type wells 61 and 62, thepotentials of the P-type wells 71 and 72 can be set to potentials ofpower supply voltages that are different to each other. However, whenthe potentials of the N-type wells 61 and 62 are set to potentials ofhigh potential-side power supply voltages, as shown in FIG. 2 , there isa risk that element breakdown or an unexpected current leakage mayoccur. In the following, this point will be described.

FIGS. 3 and 4 show a second cross-sectional view of the semiconductorsubstrate of the circuit device 101. The protection diode 21, the P-typetransistor 51, and the N-type transistor 52, of the constituent elementsof the circuit device 101, are shown in FIGS. 3 and 4 . Theconfiguration is the same between FIG. 3 and FIG. 4 . First, adescription will be given using FIG. 3 .

The circuit device 101 shown in FIG. 3 includes the P-type substrate 90,N-type wells NWA to NWC that are provided in the P-type substrate 90, aP-type well PWA provided in the N-type well NWA, and a P-type well PWCprovided in the N-type well NWC. Also, the circuit device 101 includesthe N-type transistor 52 provided on the P-type well PWA, the P-typetransistor 51 provided on the N-type well NWB, and the protection diode21 provided on the P-type well PWC.

Note that, in FIG. 3 , illustration of the cross sectional structureregarding the N-type transistor 82 in FIG. 2 is omitted. With respect tothe N-type transistor 81, the N-type well 61 and the P-type well 71 inFIG. 2 correspond to the N-type well NWA and the P-type well PWA, or theN-type well NWC and the P-type well PWC in FIG. 3 . In the latter case,the circuit element on the P-type well is a diode.

As shown in FIG. 3 , a parasitic diode DP1 is formed between the P-typewell PWA and the N-type well NWA, and a parasitic diode DP2 is formedbetween the P-type substrate 90 and the N-type well NWA. The potentialof the P-type well PWA is set to the potential of the ground powersupply voltage PGND through a p⁺ impurity region RPA, the potential ofthe N-type well NWA is set to the potential of the power supply voltageVDR through an n⁺ impurity region RNA, and the potential of the P-typesubstrate 90 is set to the potential of the ground power supply voltageAGND through the p⁺ impurity region 95. Therefore, voltagescorresponding to potential differences between the power supply voltageVDR and the ground power supply voltages are respectively applied to theparasitic diodes DP1 and DP2 as reverse voltages.

Similarly, a parasitic diode DP3 is formed between the P-type well PWCand the N-type well NWC, and a parasitic diode DP4 is formed between theP-type substrate 90 and the N-type well NWC. The potential of the P-typewell PWC is set to the potential of the ground power supply voltage PGNDthrough a p⁺ impurity region of the protection diode 21, the potentialof the N-type well NWC is set to the potential of the power supplyvoltage VDR through an n⁺ impurity region RNC, and the potential of theP-type substrate 90 is set to the potential of the ground power supplyvoltage AGND through the p⁺ impurity region 95. Therefore, voltagescorresponding to potential differences between the power supply voltageVDR and the ground power supply voltages are respectively applied to theparasitic diodes DP3 and DP4 as reverse voltages.

As described above, when a high potential-side power supply voltage isapplied to N-type wells, since reverse voltages are applied to theparasitic diodes DP1 to DP4, there is a risk that when one or more ofthe reverse voltages exceeds the respective break down voltages of theparasitic diode DP1 to DP4, an element or elements may be broken down.Therefore, this fact need to be considered in circuit design or layoutdesign such that elements will not be broken down, and as a result, thecomplexity of the circuit design or layout design increases.

FIG. 4 illustrates a current path when a negative potential that islower than the potential of the ground power supply voltage PGND isapplied to the output terminal TGATE. The cross sectional structure issimilar to that in FIG. 3 , and therefore the description thereof isomitted. For example, a case is envisioned where a negative potential isapplied to the output terminal TGATE due to noise, static electricity,or a short circuit. Alternatively, it is envisioned that a negativepotential is applied to the output terminal TGATE in a latch-up test ofthe circuit device 100. It is assumed that the gate of the P-typetransistor 51 and the gate of the N-type transistor 52 are driven to thepotential of the power supply voltage VDR by the predriver 55, theP-type transistor 51 is in an off state and the N-type transistor 52 isin an on state.

As shown in FIG. 4 , when a negative potential is applied to the outputterminal TGATE, a first current path indicated by solid-line arrows, anda second current path indicated by dotted-line arrows are formed. In thefirst current path, currents flow from the ground power supply voltagesAGND and PGND to the output terminal TGATE. Specifically, the P-typewell PWC to which the ground power supply voltage PGND is supplied is ananode of the protection diode 21, an n⁺ impurity region provided in theP-type well PWC is a cathode of the protection diode 21, and the cathodeis connected to the output terminal TGATE. Therefore, currents flow fromthe ground power supply voltages AGND and PGND to the output terminalTGATE through the protection diode 21. Also, since the N-type transistor52 is in an on state, currents flow from the ground power supplyvoltages AGND and PGND to the output terminal TGATE through the N-typetransistor 52. This first current path is usually envisioned, in designor the like, as a current path when a negative potential is applied tothe output terminal TGATE.

In the second current path, a current flows from the power supplyvoltage VDR to the output terminal TGATE. Specifically, the N-type wellNWA, the P-type well PWA, and the drain of the N-type transistor 52constitute an NPN-type parasitic bipolar transistor BTP1. The P-typewell PWA, which functions as a base, is at the potential of the groundpower supply voltage PGND, and the drain of the N-type transistor 52,which functions as an emitter, is at a negative potential, and thereforethe parasitic bipolar transistor BTP1 is turned on. With this, a currentflows from the power supply voltage VDR to the output terminal TGATEthrough the collector and emitter of the parasitic bipolar transistorBTP1. Also, the N-type well NWC, the n⁺ impurity region of theprotection diode 21, and the P-type well PWC constitute an NPN-typeparasitic bipolar transistor BTP2. The P-type well PWC, which functionsas a base, is at the potential of the ground power supply voltage PGND,and the n⁺ impurity region of the protection diode 21, which functionsas an emitter, is at a negative potential, and therefore the parasiticbipolar transistor BTP2 is turned on. With this, a current flows fromthe power supply voltage VDR to the output terminal TGATE through thecollector and emitter of the parasitic bipolar transistor BTP2.

The second current path is a path that is not usually envisioned, indesign or the like, as a current path when a negative potential isapplied to the output terminal TGATE, and therefore there is a risk thatan unexpected leak current flows in the path. This leak current mayincur an adverse effect to the circuit device 100 such as heatgeneration. Specifically, as described with reference to FIG. 1 , theregulator 30 generates the power supply voltage VDR from the input powersupply voltage VIN. Therefore, the current that flows from the powersupply voltage VDR to the output terminal TGATE incurs a current thatflows from the input power supply voltage VIN to the power supply nodeNVDR via the regulator 30. In FIG. 1 , this current flows through theP-type transistor 31, and therefore it is possible that the P-typetransistor 31 generates heat and fails.

The input power supply voltage VIN is at a higher potential than thepower supply voltage VDR, and therefore, when a power loss ofpotential×current is considered, the power loss with the input powersupply voltage VIN is larger than the power loss with the power supplyvoltage VDR. Therefore, the generated heat increases as the input powersupply voltage VIN increases. For example, as will be described laterwith reference to FIG. 9 or the like, a light source circuit that drivesa laser diode or the like is envisioned as an application example of thecircuit device 100. When a plurality of laser diodes are connected inseries in order to increase the light amount, the input power supplyvoltage VIN needs to be increased in order to deal with the voltagedrops in the laser diodes. Therefore, the power loss when a leak currentflows from the input power supply voltage VIN increases, and thegenerated heat increases.

3. Exemplary Cross Sectional Structure of Present Embodiment

FIG. 5 is a first cross-sectional view of the semiconductor substrate ofthe circuit device 100 in the present embodiment. The circuit device 100is configured as illustrated in FIG. 1 , and some of the constituentelements of the circuit device 100 are shown in FIG. 2 . Note that theconstituent elements that are the same as the constituent elements thathave been already described are given the same reference signs, and thedescription of the constituent elements will be appropriately omitted.

The circuit device 100 includes the P-type substrate 90, the N-type well61, which is the first N-type well, the N-type well 62, which is thesecond N-type well, the P-type well 71, which is the first P-type well,the P-type well 72, which is the second P-type well, the N-typetransistor 81, which is the first circuit element, and the N-typetransistor 82, which is the second circuit element. The ground powersupply voltage PGND is a first ground power supply voltage, and theground power supply voltage AGND is a second ground power supplyvoltage. Note that the first circuit element and the second circuitelement are not limited to the N-type transistors, and may also bediodes, resistors, or capacitors.

In FIG. 2 , the power supply voltage VDR is supplied to the N-type well61, but in the present embodiment, a first potential VD1 is supplied tothe N-type well 61. The first potential VD1 is a potential that isgreater than or equal to the potential of the ground power supplyvoltage PGND and is less than the potential of the power supply voltageVDR. The power supply voltage VDR is a high potential-side power supplyvoltage when the ground power supply voltage PGND is a lowpotential-side power supply voltage. The first potential VD1 is suppliedfrom a node at a power supply voltage that is not electrically connectedto a node at the power supply voltage VDR. Being “not electricallyconnected” means being not electrically connected at least in thecircuit device 100. Specifically, the “power supply voltage at a nodethat is not electrically connected to a node at the power supply voltageVDR” is a power supply voltage that is supplied by a power supply linethat is not electrically connected to the power supply line of the powersupply voltage VDR. More specifically, the power supply voltage VDR isgenerated from the input power supply voltage VIN, as described in FIG.1 , but the “power supply voltage at a node that is not electricallyconnected to a node at the power supply voltage VDR” is a power supplyvoltage that is not generated from the input power supply voltage VIN.For example, the power supply voltage is a power supply voltage suppliedfrom the outside of the circuit device 100 separately from the inputpower supply voltage VIN, or a power supply voltage generated from thepower supply voltage supplied from the outside.

In this way, the potential of the N-type well 61 can be set to anappropriate potential. That is, the power supply voltage VDR is nolonger supplied to the N-type well 61, and therefore element breakdownor an unexpected leak current can be suppressed from occurring. Thispoint will be described using FIG. 6 .

FIG. 6 is a second cross-sectional view of the semiconductor substrateof the circuit device 100. The protection diode 21, the P-typetransistor 51, and the N-type transistor 52, of the constituent elementsof the circuit device 100, are shown in FIG. 6 . Note that theconstituent elements that are the same as the constituent elements thathave been already described are given the same reference signs, and thedescription of the constituent elements will be appropriately omitted.

The circuit device 100 includes the P-type substrate 90, the N-typewells NWA, NWB, and NWC, the P-type wells PWA and PWC, the N-typetransistor 52, the P-type transistor 51, and the protection diode 21.The N-type well 61 and the P-type well 71 in FIG. 5 correspond to theN-type well NWA and the P-type well PWA, or the N-type well NWC and theP-type well PWC in FIG. 6 . The N-type well NWB is a third N-type well,and the P-type transistor 51 is a third circuit element. Note that, inFIG. 6 , the first potential VD1 is a potential of the ground powersupply voltage PGND.

As shown in FIG. 6 , the potentials of the P-type well PWA and theN-type well NWA are set to the potential of the ground power supplyvoltage PGND, and therefore reverse voltages are not applied to theparasitic diodes DP1 and DP2. Similarly, the potentials of the P-typewell PWC, the N-type well NWC, and the P-type substrate 90 are set tothe potential of the ground power supply voltage PGND, and thereforereverse voltages are not applied to the parasitic diodes DP3 and DP4.Therefore, the break down voltages of the parasitic diode DP1 to DP4need not be taken into consideration when circuit design or layoutdesign is performed, and as a result, the circuit design or the layoutdesign can be simplified.

Also, as shown in FIG. 6 , the potentials of the N-type well NWA, whichis a collector of the parasitic bipolar transistor BTP1, and the N-typewell NWC, which is a collector of the parasitic bipolar transistor BTP2are set to the potential of the ground power supply voltage PGND.Therefore, when a negative potential is applied to the output terminalTGATE, currents flow from the ground power supply voltages AGND and PGNDto the output terminal TGATE through the parasitic bipolar transistorsBTP1 and BTP2. That is, nodes at the ground power supply voltages AGNDand PGND are on upstream of the second current path described withreference to FIG. 4 , and therefore, when a negative potential isapplied to the output terminal TGATE, an unexpected leak current doesnot flow from a node at the power supply voltage VDR. With this, when anegative potential is applied to the output terminal TGATE, the powerloss due to a leak current can be suppressed, and a circuit failure dueto heat generation or the like can be suppressed.

Note that, as shown in FIG. 5 , in the present embodiment, the potentialof the N-type well 62 may be set to the potential VX. With this, areverse voltage is no longer applied to a parasitic diode that is formedbetween the P-type well 72 and the N-type well 62, and thereforeelements can be suppressed from being broken down. Also, when thepotential VX is the potential of the ground power supply voltage AGND, areverse voltage is no longer applied to a parasitic diode that is formedbetween the P-type substrate 90 and the N-type well 62, and thereforeelements can be suppressed from being broken down. Also, when thepotential VX is a potential between the ground power supply voltage AGNDand the input power supply voltage VIN, the reverse voltage of theparasitic diode decreases relative to the case where the potential ofthe N-type well 62 is set to the potential of the input power supplyvoltage VIN, and therefore the possibility of element breakdown can bereduced.

Note that, the first circuit element is an N-type transistor in FIG. 5 ,and the first circuit element is an N-type transistor or a protectiondiode in FIG. 6 , but the first circuit element is not limited thereto.FIG. 7 is a cross-sectional view of an exemplary configuration ofmodification of the first circuit element.

As shown in FIG. 7 , an N-type well NWD is provided in the P-typesubstrate 90, a P-type well PWD is provided in the N-type well NWD, anda first circuit element 83 is provided in the P-type well PWD. Thepotential of the N-type well NWD is set to the potential of the groundpower supply voltage PGND through an n⁺ impurity region RND, and thepotential of the P-type well PWD is set to the potential of the groundpower supply voltage PGND through a p⁺ impurity region RPD. The firstcircuit element 83 is a polysilicon resistor formed on the P-type wellPWD, a capacitor whose electrodes include an electrode formed by apolysilicon layer formed on the P-type well PWD, or the like.

In the configuration shown in FIG. 7 as well, although parasitic diodessimilar to the parasitic diodes DP1 to DP4 in FIG. 6 are formed, becausethe ground power supply voltage PGND is supplied to the N-type well NWD,reverse voltages are not applied to the parasitic diodes. With this,element breakdown can be suppressed. Note that the first potential VD1described in FIG. 5 may be supplied to the N-type well NWD.

4. Detailed Exemplary Configuration

FIG. 8 is a detailed cross-sectional view of the semiconductor substratein the present embodiment. Some of the constituent elements of thecircuit device 100 are shown in FIG. 8 . The circuit device 100 shown inFIG. 8 includes the P-type substrate 90, an N-type transistor NTR, and aP-type transistor PTR. Note that, in the present embodiment, “on”indicates a thickness direction of the semiconductor substrate and adirection in which films are stacked in the semiconductor process.

In the cross sectional structure of the N-type transistor NTR, an N-typeburied layer NBL1 and a P-type buried layer PBL1 are provided on theP-type substrate 90. The buried layer is a layer that is buried in thesubstrate by forming an epitaxial layer on the layer. A deep N-type wellDNWELL1 is provided on the N-type buried layer NBL1, and the N-typeburied layer NBL1 is in contact with the deep N-type well DNWELL1. Thedeep well is a well provided under a P-type well or an N-type well. Thedeep N-type well DNWELL1 and the N-type buried layer NBL1 are providedin a region covering depths substantially the same as the P-type buriedlayer PBL1. The N-type buried layer NBL1 need not cover the entirety ofthe deep N-type well DNWELL1. That is, some of the deep N-type wellDNWELL1 may be in contact with the P-type substrate 90.

A P-type well PWELL1 and an N-type well NWELL1 are provided on the deepN-type well DNWELL1, and the P-type well PWELL1 and the N-type wellNWELL1 are in contact with the deep N-type well DNWELL1. A P-type wellPWELL2 is provided on the P-type buried layer PBL1, and the P-type wellPWELL2 is in contact with the P-type buried layer PBL1. The P-type wellPWELL1 is in contact with the N-type well NWELL1, and the N-type wellNWELL1 is in contact with the P-type well PWELL2.

N⁺ impurity regions RN1 and RN2 and a P⁺ impurity region RP1 areprovided on the P-type well PWELL1, and these impurity regions reachsurfaces of the P-type well PWELL1 and the P-type substrate 90. An N⁺impurity region RN3 is provided on the N-type well NWELL1, and the N⁺impurity region RN3 reaches the surfaces of the N-type well NWELL1 andthe P-type substrate 90. A P⁺ impurity region RP2 is provided on theP-type well PWELL2, and the P⁺ impurity region RP2 reaches the surfacesof the P-type well PWELL2 and the P-type substrate 90. Insulating layersIS1 to IS5 are provided as insulating layers for isolating adjacentimpurity regions.

The P-type well PWELL1 reaches the surface of the P-type substrate 90 ina region between the N⁺ impurity regions RN1 and RN2, and a gate GT1formed by a polysilicon layer is provided thereon. For example, a metallayer connected to the N⁺ impurity region RN1 is a source SS1 of theN-type transistor NTR, and a metal layer connected to the N⁺ impurityregion RN2 is a drain DR1 of the N-type transistor NTR.

The P⁺ impurity region RP2 is connected to a node at the ground powersupply voltage AGND. With this, the potential of the P-type substrate 90is set to the potential of the ground power supply voltage AGND throughthe P-type well PWELL2 and the P-type buried layer PBL1.

The potentials of the P⁺ impurity region RP1 and the N⁺ impurity regionRN3 are set to the potential of the ground power supply voltage PGND.With this, the potentials of the P-type well PWELL1, the N-type wellNWELL1, the deep N-type well DNWELL1, and the N-type buried layer NBL1are set to the potential of the ground power supply voltage PGND. TheN-type well NWELL1, the deep N-type well DNWELL1, and the N-type buriedlayer NBL1 correspond to the N-type well 61 in FIG. 5 , and the N-typewell NWA in FIG. 6 .

In the cross sectional structure of the P-type transistor PTR, an N-typeburied layer NBL2 and a P-type buried layer PBL2 are provided on theP-type substrate 90. A deep N-type well DNWELL2 is provided on theN-type buried layer NBL2, and the N-type buried layer NBL2 is in contactwith the deep N-type well DNWELL2. The deep N-type well DNWELL2 and theN-type buried layer NBL2 are provided in a region covering depthssubstantially the same as the P-type buried layer PBL2. The N-typeburied layer NBL2 need not cover the entirety of the deep N-type wellDNWELL2. That is, some of the deep N-type well DNWELL2 may be in contactwith the P-type substrate 90.

An N-type well NWELL2 is provided on the deep N-type well DNWELL2, andthe N-type well NWELL2 is in contact with the deep N-type well DNWELL2.A P-type well PWELL3 is provided on the P-type buried layer PBL2, andthe P-type well PWELL3 is in contact with the P-type buried layer PBL2.The N-type well NWELL3 is in contact with the P-type well PWELL3.

P⁺ impurity regions RP3 and RP4 and an N⁺ impurity region RN4 areprovided on the N-type well NWELL2, and these impurity regions reachsurfaces of the N-type well NWELL2 and the P-type substrate 90. A P⁺impurity region RP5 is provided on the P-type well PWELL3, and the P⁺impurity region RP5 reaches surfaces of P-type well PWELL3 and theP-type substrate 90. Insulating layers IS6 to IS9 are provided asinsulating layers for isolating adjacent impurity regions.

The N-type well NWELL2 reaches the surface of the P-type substrate 90 ina region between the P⁺ impurity regions RP3 and RP4, and a gate GT2formed by a polysilicon layer is provided thereon. For example, a metallayer connected to the P⁺ impurity region RP3 is a drain DR2 of theP-type transistor PTR, and a metal layer connected to the P⁺ impurityregion RP4 is a source SS2 of the P-type transistor PTR.

The P⁺ impurity region RP5 is connected to the node at the ground powersupply voltage AGND. With this, the potential of the P-type substrate 90is set to the potential of the ground power supply voltage AGND throughthe P-type well PWELL3 and the P-type buried layer PBL2.

The potentials of the N⁺ impurity region RN4 is set to the potential ofthe power supply voltage VDR. With this, the potentials of the N-typewell NWELL2, the deep N-type well DNWELL2, and the N-type buried layerNBL2 are set to the potential of the power supply voltage VDR. TheN-type well NWELL2, the deep N-type well DNWELL2, and the N-type buriedlayer NBL2 correspond to the N-type well NWB in FIG. 6 .

5. Light Source Device

FIG. 9 shows a first exemplary configuration of a light source device200 including the circuit device 100, and FIG. 13 shows an exemplaryconfiguration of a light source circuit 10. The light source device 200includes the circuit device 100 and the light source circuit 10. Thecircuit device 100 in the light source device 200 may also be referredto as a light emission control device.

The light source circuit 10 includes a first switching element 11, asecond switching element 12, an inductor 14, and a light emittingelement 15. Also, the light source circuit 10 includes a first resistorRCS, a second resistor RIS, a capacitor CA, and a diode DA1. The firstswitching element 11 and the second switching element 12 are N-typetransistors.

The light emitting element 15 is driven by a current ILD, and emitslight at a brightness corresponding to the current value of the currentILD. The light emitting element 15 is constituted by a plurality oflaser diodes connected in series. Note that the light emitting element15 may also be constituted by one laser diode, or an LED (Light EmittingDiode).

The light emitting element 15 and the first switching element 11 areprovided in series between a first power supply node NVI and a firstnode N1. The first power supply node NVI is a node to which the inputpower supply voltage VIN is to be input. The first node N1 is a nodethat is connected to one end of the inductor 14. The inductor 14, thesecond switching element 12, and the second resistor RIS are provided inseries between the first node N1 and a second power supply node NGN. Thesecond power supply node NGN is a node to which the ground power supplyvoltage PGND is to be input. The capacitor CA is provided between thefirst power supply node NVI and the first node N1. The diode DA1 isprovided between the first power supply node NVI and the other end ofthe inductor 14. Also, the light source circuit 10 may includecapacitors CB and CC, a diode DA2, a diode DB, a Zener diode DC, and aresistor RA. These elements are provided in order to control the gatevoltage of the first switching element 11.

The second switching element 12 is for controlling the current flowingthrough the inductor 14 through switching regulation. The firstswitching element 11 is for controlling whether or not the currentflowing through the inductor 14 is allowed to flow through the lightemitting element 15. A mode in which the first switching element 11 iscontinuously turned on, and the light emission amount of the lightemitting element 15 is controlled by controlling the second switchingelement 12 through switching regulation is referred to as an analoglight modulation mode. Also, a mode in which the first switching element11 is repeatedly turned on and off, and the light emission amount of thelight emitting element 15 is controlled by the on duty ratio is referredto as a PWM light modulation mode.

The circuit device 100 includes a first drive circuit 110, a seconddrive circuit 112, a first control circuit 114, a second control circuit120, power supply circuits 191 to 193, a PWM terminal TDCS, a lightmodulation voltage input terminal TACS, and terminals TVIN, TDRV, TGTB,TGTB′, TIS, TCSP, and TCSN. The first drive circuit 110 or the seconddrive circuit 112 corresponds to the drive circuit 50 in FIG. 1 , theterminal TDRV, TGTB, or TGTB′ corresponds to the output terminal TGATEin FIG. 1 , and the power supply circuit 191 corresponds to theregulator 30 in FIG. 1 .

The input power supply voltage VIN is input to the terminal TVIN from apower supply circuit provided outside the circuit device 100. The powersupply circuit 191 converts the potential of the input power supplyvoltage VIN to the potential of the power supply voltage VDR, andsupplies the power supply voltage VDR to the first drive circuit 110 andthe second drive circuit 112. The power supply circuit 192 converts thepotential of the input power supply voltage VIN to the potential of thepower supply voltage VDL, and supplies the power supply voltage VDL tothe first control circuit 114. The power supply circuit 193 converts thepotential of the input power supply voltage VIN to the potential of thepower supply voltage VDA, and supplies the power supply voltage VDA tothe second control circuit 120. Each of the power supply circuits 191 to193 is a regulator, and is a linear regulator using a non-invertingamplifier circuit, for example.

A PWM signal DCS to be used for light modulation control in the PWMlight modulation mode is input to the PWM terminal TDCS from aprocessing device. A light modulation voltage ACS to be used for lightmodulation control in the analog light modulation mode is input to thelight modulation voltage input terminal TACS from the processing device.The processing device is a host device of the circuit device 100, and isa processor such as an MPU or a CPU, for example.

The first control circuit 114 outputs a first control signal based onthe PWM signal DCS. The first control circuit 114 is a logic circuitthat operates with the power supply voltage VDL, and is a buffer circuitfor buffering the PWM signal DCS, for example.

The first drive circuit 110 is a driver for driving the first switchingelement 11, and operates with the power supply voltage VDR. The firstdrive circuit 110 outputs the first drive signal DRV based on the firstcontrol signal from the first control circuit 114. The first drivesignal DRV is a signal for controlling turning on and off of the firstswitching element 11. The first drive signal DRV is output from theterminal TDRV, and is input to a gate of the first switching element 11.The first drive circuit 110 outputs the first drive signal DRV forturning on the first switching element 11 when the PWM signal DCS isactivated, and outputs the first drive signal DRV for turning off thefirst switching element 11 when the PWM signal DCS is inactivated.

The second control circuit 120 outputs a second control signal based onthe light modulation voltage ACS and the PWM signal DCS. The secondcontrol circuit 120 is an analog circuit that operates with the powersupply voltage VDA. The second control circuit 120 controls turning onand off of the second switching element 12 in a period in which the PWMsignal DCS is activated. Specifically, a voltage CSP at one end of thefirst resistor RCS is input to the terminal TCSP, a voltage CSN at theother end of the first resistor RCS is input to the terminal TCSN, and avoltage IS of one end of the second resistor RIS is input to theterminal TIS. The second control circuit 120 controls the current ILDflowing through the light emitting element 15 so as to correspond to thelight modulation voltage ACS by controlling the current ILD throughswitching regulation based on the voltages CSP, CSN, and IS and thelight modulation voltage ACS.

The second drive circuit 112 is a driver for driving the secondswitching element 12, and operates with power supply voltage VDR. Thesecond drive circuit 112 outputs a second drive signal GTB and a signalGTB′ based on the second control signal from the second control circuit120. The second drive signal GTB is a signal for controlling turning onand off of the second switching element 12. The second drive signal GTBis output from the terminal TGTB, and is input to a gate of the secondswitching element 12. The signal GTB′ is output from the terminal TGTB′.The signal GTB′ is a signal for controlling the gate voltage of thefirst switching element 11. The signal GTB′ is a signal having the samewaveform as the second drive signal GTB, for example, but may also be asignal having a different waveform from the second drive signal GTB.

FIG. 10 is a waveform diagram in the PWM light modulation mode. Thecycle of the PWM signal DCS is denoted by TPWM, and the period in whichthe PWM signal DCS is at a high level is denoted by THW. The duty ratioof the PWM signal DCS is (THW/TPWM)×100%.

When the PWM signal DCS is at a high level, the first drive circuit 110outputs the first drive signal DRV at a high level. With this, the firstswitching element 11 is turned on. Here, the second control circuit 120and the second drive circuit 112 perform the switching regulationcontrol by switching the second switching element 12. With this, thecurrent ILD corresponding to the light modulation voltage ACS flowsthrough the light emitting element 15. When the PWM signal DCS is at alow level, the first drive circuit 110 outputs the first drive signalDRV at a low level. With this, the first switching element 11 is turnedoff. Also, the second control circuit 120 and the second drive circuit112 turn off the second switching element 12. Here, current does notflow through the light emitting element 15.

The average over time of the current ILD flowing through the lightemitting element 15 is determined by the duty ratio of the PWM signalDCS, and therefore the light emission amount is also determined by theduty ratio of the PWM signal DCS. As described above, in the PWM lightmodulation mode, light modulation control is performed using the dutyratio of the PWM signal DCS. In the analog light modulation mode, thePWM signal DCS that is continuously at a high level is input to the PWMterminal TDCS. The operations of the circuit device 100 in the analoglight modulation mode is similar to those of the circuit device 100 whenthe PWM signal DCS is at a high level in the PWM light modulation mode.That is, in the analog light modulation mode, since the current ILDcorresponding to the light modulation voltage ACS flows through thelight emitting element 15, light modulation control is performed by thelight modulation voltage ACS.

FIG. 11 shows a second exemplary configuration of the light sourcedevice 200 including the circuit device 100. Note that the constituentelements that have been described with reference to FIG. 9 are given thesame reference signs, and the description of the constituent elementswill be appropriately omitted.

In FIG. 11 , a P-type transistor 16 is provided as a first switchingelement. A source of the P-type transistor 16 is connected to the firstpower supply node NVI to which the input power supply voltage VIN is tobe input. Also, in FIG. 11 , the circuit device 100 includes a powersupply circuit 194. The power supply circuit 194 generates a powersupply voltage VHB from the input power supply voltage VIN. Thepotential of the power supply voltage VHB is a potential that causes theP-type transistor 16 to turn on, and is lower than the potential of theinput power supply voltage VIN and higher than the potential of theground power supply voltage PGND. The high potential-side power supplyvoltage of the first drive circuit 110 is the input power supply voltageVIN, and the low potential-side power supply voltage thereof is thepower supply voltage VHB.

In the configuration shown in FIG. 11 , the power supply voltage VHB issupplied to a source of an N-type transistor in the first drive circuit110, and the ground power supply voltage PGND is supplied to a source ofan N-type transistor in the second drive circuit 112. Although the powersupply voltage VHB and the ground power supply voltage PGND aredifferent power supply voltages, as a result of isolating N-typetransistors by N-type wells, as described with reference to FIG. 5 andthe like, the above-described two types of N-type transistors can beprovided. Note that when the circuit device 100 is configured asdescribed in FIG. 11 , the potential VX in FIGS. 2 and 5 corresponds tothe power supply voltage VHB.

6. Electronic Apparatus

FIG. 12 shows an exemplary configuration of an electronic apparatus 400including the light source device 200. A projection type video displaydevice is shown in FIG. 12 as an example of the electronic apparatus400. The projection type video display device is a device that projectsa video on a screen, and is also referred to as a projector. Theelectronic apparatus 400 includes a light source device 200, aprocessing device 300, an operation unit 310, a storage unit 320, acommunication unit 330, a display device 340, and an optical system 350.The light source device 200 includes the circuit device 100 and thelight source circuit 10.

The communication unit 330 communicates with an information processingdevice such as a PC. The communication unit 330 is one or more ofvarious types of video interfaces conforming to the VGA standard, theDVI standard, the HDMI (registered trade mark) standard. Alternatively,the communication unit 330 may be a communication interface such as theUSB standard, or may also be a network interface such as a LAN. Thestorage unit 320 stores image data input from the communication unit330. Also, the storage unit 320 may also function as a working memory ofthe processing device 300. The storage unit 320 is one or more ofvarious storage devices such as a semiconductor memory and a hard diskdrive. The operation unit 310 is a user interface for a user to operatethe electronic apparatus 400. For example, the operation unit 310 is abutton, a touch panel, a pointing device, a character input device, orthe like. The processing device 300 is a processor such as a CPU or anMPU. The processing device 300 transmits image data stored in thestorage unit 320 to the display device 340. Also, the processing device300 performs light modulation control by outputting a PWM signal and alight modulation voltage to the circuit device 100. The display device340 includes a liquid crystal display panel and a display driver thatcauses the liquid crystal display panel to display an image based on theimage data. Light from the light source circuit 10 is incident on theliquid crystal display panel, and the light that has passed through theliquid crystal display panel is projected on the screen by the opticalsystem 350. In FIG. 12 , the light path is indicated by dotted-linearrows.

The circuit device of the present embodiment described above includes afirst N-type well on a P-type substrate, a first P-type well provided inthe first N-type well, a first circuit element provided in the firstP-type well, a second N-type well on the P-type substrate, a secondP-type well provided in the second N-type well, and a second circuitelement provided in the second P-type well. A first ground power supplyvoltage is supplied to the first P-type well. A power supply voltagedifferent from the first ground power supply voltage is supplied to thesecond P-type well. The first ground power supply voltage or a firstpotential that is greater than or equal to the potential of the firstground power supply voltage and less than the potential of a highpotential-side power supply voltage is supplied to the first N-typewell.

According to the present embodiment, since the first ground power supplyvoltage or the first potential is supplied to the first N-type well, thepotential of the first N-type well 61 can be set to an appropriatepotential. That is, because the potential supplied to the first N-typewell is lower than the potential of the high potential-side power supplyvoltage, element breakdown can be suppressed from occurring. Also, acurrent path from the high potential-side power supply voltage to thefirst N-type well disappear, and therefore the occurrence of anunexpected leak current flowing from the high potential-side powersupply voltage to the first N-type well can be suppressed.

Also, in the present embodiment, a second ground power supply voltagedifferent from the first ground power supply voltage may be supplied tothe second P-type well.

According to the present embodiment, the first P-type well is isolatedfrom the P-type substrate by the first N-type well, and the secondP-type well is isolated from the P-type substrate by the second N-typewell. With such a triple well structure, different ground power supplyvoltages can be respectively supplied to the first P-type well and thesecond P-type well. In the present embodiment, the potentials of theN-type wells in such a triple well structure can be set to appropriatepotentials.

Also, in the present embodiment, the first circuit element may be anN-type transistor having a source supplied with the first ground powersupply voltage.

According to the present embodiment, an N-type transistor having atriple well structure is configured, and the potential of the N-typewell of the triple well structure can be appropriately set.

Also, in the present embodiment, an output terminal connected to a drainof the N-type transistor may be included.

A parasitic bipolar transistor is formed in the N-type transistor havinga triple well structure. The collector of the parasitic bipolartransistor is the first N-type well, the emitter is the drain of theN-type transistor, and the base is the first P-type well. When anegative potential is applied to the output terminal connected to thedrain of the N-type transistor, a leak current flows from the collectorto the emitter of the parasitic bipolar transistor. In the presentembodiment, since the first ground power supply voltage or the firstpotential is supplied to the first N-type well, which is a collector, anunexpected leak current will not flow from a node at the highpotential-side power supply voltage through the parasitic bipolartransistor.

Also, in the present embodiment, the circuit device may be provided witha third N-type well that is provided in the P-type substrate, and issupplied with a high potential-side power supply voltage, and a thirdcircuit element provided in the third N-type well.

With this, a third circuit element provided in a third N-type well canbe provided along with the first circuit element and the second circuitelement having the triple well structure.

Also, in the present embodiment, the third circuit element may be aP-type transistor having a source supplied with the high potential-sidepower supply voltage.

With this, a P-type transistor provided in the third N-type well can beprovided along with the first circuit element and the second circuitelement having the triple well structure.

Also, in the present embodiment, the circuit device may include aregulator. The regulator may generate the high potential-side powersupply voltage based on an input power supply voltage whose potential ishigher than the potential of the high potential-side power supplyvoltage, and supply the generated high potential-side power supplyvoltage to the source of the P-type transistor.

In the present embodiment, if a leak current flows through a node at thehigh potential-side power supply voltage, the leak current flows to anode at the input power supply voltage via the regulator. Since thepotential of the input power supply voltage is higher than the potentialof the high potential-side power supply voltage, the power loss due tothe leak current increases, and there is a risk that heat generation orthe like may occur due to the power loss. In the present embodiment, asa result of the potential of the first N-type well being set to anappropriate potential, an unexpected leak current will not flow from anode at the high potential-side power supply voltage, and heatgeneration or the like due to power loss can be suppressed.

Also, in the present embodiment, the first circuit element may be aprotection diode. In the protection diode, the first P-type well may bea cathode, and an N-type impurity region provided in the first P-typewell may be an anode.

A parasitic bipolar transistor is formed in the protection diode havinga triple well structure. The collector of the parasitic bipolartransistor is the first N-type well, the emitter is the N-type impurityregion, and the base is the first P-type well. When a negative potentialis applied to the output terminal connected to the cathode of theprotection diode, a leak current flows from the collector to the emitterof the parasitic bipolar transistor. In the present embodiment, sincethe first ground power supply voltage or the first potential is suppliedto the first N-type well, which is a collector, an unexpected leakcurrent will not flow from a node at the high potential-side powersupply voltage through the parasitic bipolar transistor.

Also, in the present embodiment, the first potential may be supplied tothe first N-type well from a node, at a power supply voltage, that isnot electrically connected to a node at the high potential-side powersupply voltage.

As a result of the first potential being supplied from a node, at apower supply voltage, that is not electrically connected to a node atthe high potential-side power supply voltage, even if a leak currentflows through the first N-type well, an unexpected leak current will notflow from a node at the high potential-side power supply voltage.

Also, in the present embodiment, the circuit device may include a thirdN-type well provided in the P-type substrate, a P-type transistorprovided in the third N-type well, and an output terminal. The highpotential-side power supply voltage may be supplied to the third N-typewell. The high potential-side power supply voltage may be supplied to asource of the P-type transistor. The first circuit element may be anN-type transistor having a source supplied with the first ground powersupply voltage. The drain of the P-type transistor and the drain of theN-type transistor are connected to the output terminal, and the P-typetransistor and the N-type transistor may constitute a driver foroutputting an output signal to the output terminal.

In the present embodiment, a parasitic bipolar transistor is formed inthe N-type transistor of the driver. A collector of the parasiticbipolar transistor is the first N-type well, an emitter is the drain ofthe N-type transistor, and a base is the first P-type well. In thepresent embodiment, the first ground power supply voltage or the firstpotential is supplied to the first N-type well, which is a collector.With this, even if a negative potential is applied to the outputterminal connected to a drain of the N-type transistor, an unexpectedleak current will not flow from a node at the high potential-side powersupply voltage through the parasitic bipolar transistor.

Also, in the present embodiment, the driver may also be a driver fordriving a transistor in a light source circuit.

According to the present embodiment, in a driver that drives atransistor in a light source circuit, the potential of an N-type well ofan N-type transistor having a triple well structure can be set to anappropriate potential.

Also, the light source device of the present embodiment includes acircuit device described above, and a light source circuit.

Also, an electronic apparatus of the present embodiment includes any ofthe circuit devices described above.

Note that although an embodiment has been described in detail above, aperson skilled in the art will readily appreciate that it is possible toimplement numerous variations and modifications that do not departsubstantially from the novel aspects and effect of the disclosure.Accordingly, all such variations and modifications are also to beincluded within the scope of the disclosure. For example, terms that areused within the description or drawings at least once together withbroader terms or alternative synonymous terms can be replaced by thoseother terms at other locations as well within the description ordrawings. Also, all combinations of the embodiment and variations arealso encompassed in the range of the disclosure. Moreover, theconfiguration and operation of the circuit device, the light sourcecircuit, the light source device, and the electronic apparatus, and thelike are not limited to those described in the present embodiment, andvarious modifications are possible.

What is claimed is:
 1. A circuit device comprising: a first N-type wellon a P-type substrate; a first P-type well that is provided in the firstN-type well, wherein a first ground power supply voltage is supplied tothe first P-type well; a first circuit element provided in the firstP-type well; a second N-type well on the P-type substrate; a secondP-type well that is provided in the second N-type well, wherein a powersupply voltage different from the first ground power supply voltage issupplied to the second P-type well; and a second circuit elementprovided in the second P-type well, wherein the first ground powersupply voltage or a first potential that is (i) greater than or equal tothe potential of the first ground power supply voltage and (ii) lessthan the potential of a high potential-side power supply voltagesupplied to a node of the circuit device is supplied to the first N-typewell from a node that is not electrically connected to the node of thehigh potential-side power supply voltage, a second ground power supplyvoltage different from the first ground power supply voltage is suppliedto the second P-type well; and a coupling circuit provided between thefirst ground power supply voltage and the second ground power supplyvoltage.
 2. The circuit device according to claim 1, wherein the firstcircuit element is an N-type transistor having a source supplied withthe first ground power supply voltage.
 3. The circuit device accordingto claim 2, further comprising an output terminal connected to a drainof the N-type transistor.
 4. The circuit device according to claim 1,further comprising: a third N-type well that is provided in the P-typesubstrate, and is supplied with the high potential-side power supplyvoltage; and a third circuit element provided in the third N-type well.5. The circuit device according to claim 4, wherein the third circuitelement is a P-type transistor having a source supplied with the highpotential-side power supply voltage.
 6. The circuit device according toclaim 5, further comprising a regulator that generates the highpotential-side power supply voltage based on an input power supplyvoltage whose potential is higher than the potential of the highpotential-side power supply voltage, and supply the generated highpotential-side power supply voltage to the source of the P-typetransistor.
 7. The circuit device according to claim 1, wherein thefirst circuit element is a protection diode whose cathode is formed froma P-type impurity region provided in the first P-type well and whoseanode is formed from an N-type impurity region provided in the firstP-type well.
 8. The circuit device according to claim 1, wherein thefirst potential is supplied to the first N-type well from a node, at apower supply voltage, that is not electrically connected to a node atthe high potential-side power supply voltage.
 9. The circuit deviceaccording to claim 1, further comprising: a third N-type well that isprovided in the P-type substrate, and is supplied with a highpotential-side power supply voltage; a P-type transistor that isprovided in the third N-type well, and has a source supplied with thehigh potential-side power supply voltage; and an output terminal,wherein the first circuit element is an N-type transistor having asource supplied with the first ground power supply voltage, and thedrain of the P-type transistor and the drain of the N-type transistorare connected to the output terminal, and the P-type transistor and theN-type transistor constitute a driver for outputting an output signal tothe output terminal.
 10. The circuit device according to claim 9,wherein the driver is a driver for driving a transistor in a lightsource circuit.
 11. A light source device comprising: the circuit deviceaccording to claim 10; and the light source circuit.
 12. An electronicapparatus comprising the circuit device according to claim
 1. 13. Acircuit device comprising: a first N-type well on a P-type substrate; afirst P-type well that is provided in the first N-type well, wherein afirst ground power supply voltage is supplied to the first P-type well;a first circuit element provided in the first P-type well; a secondN-type well on the P-type substrate; a second P-type well that isprovided in the second N-type well, wherein a second power supplyvoltage different from the first ground power supply voltage is suppliedto the second P-type well; and a second circuit element provided in thesecond P-type well, wherein the first ground power supply voltage issupplied to the first N-type well, a second ground power supply voltagedifferent from the first ground power supply voltage is supplied to thesecond P-type well; and a coupling circuit provided between the firstground power supply voltage and the second ground power supply voltage.